Comparison of narrowband ultraviolet B exposure and oral vitamin D substitution on serum 25-hydroxyvitamin D concentration

BACKGROUND: A short course of narrowband ultraviolet B (NB-UVB) exposures increases the serum 25-hydroxyvitamin D [25(OH)D] concentration in patients with psoriasis and healthy subjects. OBJECTIVES: To compare the effects of NB-UVB and oral vitamin D substitution in healthy subjects in winter. METHODS: Healthy adult hospital employees and medical students were screened for serum 25(OH)D concentration. Those with 25(OH)D below 75 nmol L(-1) were randomly given either 12 NB-UVB exposures or 20 μg of oral cholecalciferol daily for 4 weeks. The NB-UVB exposures were given with a Waldmann UV 7001 cabin and the mean cumulative dose was 48·4 standard erythema doses. Serum 25(OH)D was measured before and after the treatments by radioimmunoassay. RESULTS: The baseline serum 25(OH)D concentrations were 52·9 ± 10·4 (mean ± SD) in the 33 NB-UVB-treated and 53·5 ± 12·7 nmol L(-1) in the 30 oral cholecalciferol-treated subjects. The mean increase in serum 25(OH)D was 41·0 nmol L(-1) [95% confidence interval (CI) 34·8-47·2; P < 0·001] in the NB-UVB group and 20·2 nmol L(-1) (95% CI 14·6-26·0; P < 0·001) in the cholecalciferol group. The difference between the two treatments was significant at 2 weeks (P = 0·033) and at 4 weeks (P < 0·001). One month after the treatments the 25(OH)D concentrations had increased further. CONCLUSIONS: The present study shows that 12 NB-UVB exposures given during 4 weeks increase serum 25(OH)D concentration significantly more than 20 μg of oral cholecalciferol daily. A short NB-UVB course is an effective way to improve vitamin D balance in winter and the response is still evident 2 months after the course.